Research is currently in progress on factors affecting sexual maturation in female mammals, and house mice in particular. Single-factor experiments are used to assess the influence of various social and climatic factors on puberty. Results indicate that mice mature later at cooler temperatures and earlier when housed in warmer environments. A multi-factor experiment will be conducted to assess the relative importance of male presence, female density, daylength and temperature on puberty. A second line of research seeks to ascertain the role of inheritance in determining the timing of sexual maturation. After three generations of selection two sub-lines have been developed, one of which exhibits maturation significantly earlier and one significantly later than control stocks. These sublines will eventually be used in studies of social factors affecting puberty. A third line of investigation is exploring mechanisms underlying production of the maturation-delaying pheromone found in urine from grouped females. The pheromone is not dependent upon ovarian hormones and is present in both excreted and bladder urine of all grouped females regardless of whether they are intact or ovariectomized. Two new findings were made with regard to acceleration of maturation in young females when housed with an adult male. The acceleration appears to have at least three components; a urinary pheromone, synergistic social stimulation from the male and body warmth provided by the male. A urinary pheromone is present in the both bladder and excreted urine from adult intact males, but is absent from both bladder and excreted urine of castrated males and prepubertal males. Lastly, a separate sequence of experiments revealed that both litter size and sex composition affect puberty.